Hoarding Disorder (HD) is a common, chronic and debilitating psychiatric disorder that disproportionately affects older adults, and has a profound public health impact on individuals, families and society. While safety risks associated with clutter in HD has been consistently documented (i.e. up to 25% of deaths by house fire are due to hoarding), the true extent of disability in this patient population is not known. Further, factors contributing to disability in older adults with HD, including cognitive factors, have not been adequately clarified. Emerging data, including work from our group, suggest that deficits in specific cognitive domains are common across the lifespan in HD. This project will examine the functional impact of HD in older adults ? specifically, the relationships among cognitive functioning, hoarding symptom severity, and disability. Further, we will assess the genetic risk profile of HD, and the association of HD with medical and psychiatric comorbidities that also impact disability. To achieve our aims, we will combine in-person clinical, neuropsychological, and medical frailty assessments with a unique epidemiologic resource, the online Brain Health Registry (BHR; www.brainhealthregistry.org). The BHR, which was designed to accelerate participation in clinical trials of aging and aging- related disorders, has, in three years, enrolled over 54,000 subjects who are expressly interested in participating in ongoing research with 1000 new participants enrolling every month. Nearly half (47%) of participants are ages 60 and older. Participants are well characterized in regard to psychiatric, neurological, family and medical history, and are followed longitudinally with re-assessments every six months. Identifying factors related to disability in older adults with HD will inform the development of more effective treatment interventions in this vulnerable population and offers significant promise for improving quality of life.